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HelpTest Code LAB2360 Mixing Studies
Useful For
Detecting the presence of coagulation factor deficiencies and the presence of nonspecific inhibitors. Deficiency or inhibition of coagulation factors can prolong PT and/or PTT results.
Methodology
Clot Detection
Profile Information
| Test Code | Test Name |
Available Separately |
Always Performed |
|---|---|---|---|
| LAB320 | Protime/INR | Yes | Yes |
| LAB325 | Activated Partial Thromboplastin Time (APTT) | Yes | Yes |
Testing Algorithm:
If the PT is prolonged >3SD of the normal range, a Protime Mixing Study will be performed at an additional charge.
If the APTT is prolonged >3SD of the normal range, an APTT Mixing study will be performed at an additional charge. A thrombin time will be performed to rule out the presence of heparin.
Reflex Tests
| Test Code | Test Name | Test Components |
|---|---|---|
| LAB2360 | Protime Mixing Study | PT Patient Plasma/Normal Plasma 1:1 Mix |
| PT Patient Plasma/Factor Diluent 1:1 Mix | ||
| Interpretation | ||
| APTT Mixing Study | PTT Patient Plasma/Normal Plasma Mix 1:1 Mix | |
| PTT Patient Plasma/Factor Diluent Mix 1:1 | ||
| Thrombin Time | ||
| Interpretation |
Performing Laboratory
Bozeman Health Laboratory Services
Specimen Requirements
Specimen must arrive and be tested within 4 hours of draw.
Specimen Type: Whole blood
Container/Tube: Blue top (3.2% sodium citrate)
Specimen Volume: 2 full tubes
Specimen Minimum Volume: 1 full tube
Collection Instructions:
1. Immediately after draw, invert tubes several times to mix blood with additive.
2. Send specimen in original tube.
3. If there is a delay in transport of >4 hours, specimen must be double-centrifuged to prepare a platelet-free plasma specimen as follows:
a. Immediately centrifuge at 3,200 rpm for 15 minutes.
b. Carefully remove plasma from cells avoiding platelet/buffy coat, and transfer plasma into a plastic tube.
c. Centrifuge plastic tube at 3,200 rpm for 15 minutes.
d. Carefully remove top portion of plasma and transfer plasma into a plastic tube leaving approximately 250 mcL in bottom to discard.
e. Double-centrifuged plasma should be aliquoted (0.5 mL-1 mL each) into clearly labeled plastic tubes. (Glass vial is not acceptable)
f. Plasma specimens should be frozen at <-40° C, if possible, and sent together in same container with at least 5 lbs of dry ice. Specimens must arrive in a frozen state.
4. If the patient has a hematocrit of >55 (within the last 14 days):
a. A new 'Adjust Tube' will automatically be ordered.
b. Phlebotomist or RN should contact the lab to obtain a tube with the correct anticoagulant ratio.
c. The lab will mark the tube appropriately as 'adjusted'.
d. Tube will be sent by the lab to the phlebotomist or RN to draw the patient.
e. Process the 'adjusted' tube as stated above in steps 1-3.
Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
Specimen Transport Temperature
Ambient (whole blood) <4 hours/Frozen (plasma) >4 hours
Specimen Stability
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole Blood (unspun) | Ambient | 4 hours |
| Plasma Na Citrate | Ambient | 4 hours |
| Plasma Na Citrate (double spun) | Frozen | 14 days |
Reference Values
| Component | Normal Range |
Mixing Study Reflex Value |
Critical Values |
|---|---|---|---|
| PT | 12.0-14.5 seconds | ≥ 15.6 | |
| INR | 0.9-1.1 | >5.0 | |
| PTT | 24-35 seconds | ≥ 38.2 | >100 seconds |
| Thrombin Time | 15.0-18.0 seconds |
If the result obtained with the immediate normal plasma mixture shows only partial or no correction, and the result obtained with the diluent mixture shows near correction to the reference range or only mild prolongation, then a non-specific inhibitor such as lupus anticoagulant (LA) is suspected. Plasma suspected of containing LA should be further tested with LA specific tests to confirm the presence of lupus anticoagulant.
Some inhibitors will demonstrate a delayed type inhibitor pattern, with time and/or temperature dependence. In cases with a delayed type inhibitor, the APTT immediate mix will correct to within the reference range, however, the APTT incubated mix will be prolonged. Although rare, the presence of a factor inhibitor, such as a factor VIII inhibitor, will increase the risk of life-threatening bleeding. The presence of a factor inhibitor can be confirmed by a Bethesda assay for that factor.
Day(s) Test Set Up
Monday through Sunday
Test Classification and CPT Coding
85610 PT
85611 PT plasma fraction (if needed)
85730 PTT
85732 PTT plasma fraction (if needed)
85670 Thrombin Time (if needed)
80500-Pathology Interp (if needed)